The invention relates to a process for preparing polyfluorochlorocarboxylic acid chlorides and perfluorocarboxylic acid chlorides, particularly trifluoroacetyl chloride and chlorodifluoroacetyl chloride.
Polyfluorochloro- and perfluorocarboxylic acid chlorides are building blocks in chemical synthesis, for example for producing surfactants, pharmaceuticals and agrichemicals.
Chlorodifluoroacetyl chloride is an intermediate which can be used in a variety of ways in chemical synthesis. For example, it can be used in the production of dyes. Alkyl and aryl halides can be trifluoromethylated by a derivative of chlorodifluoroacetyl chloride, namely by the methyl ester, in the presence of potassium fluoride and copper iodide. Chlorodifluoroacetyl chloride has hitherto been prepared as described in U.S. Pat. No. 3,725,475, by solvolysis of CF.sub.2 ClCCl.sub.3 with oleum or SO.sub.3 in the presence of mercury compounds and chlorinated sulfur oxides. The aforementioned methyl ester is also a precursor for the preparation of difluorocarbene, see G. A. Wheaton, D. J. Burton in J. Fluorine Chem. 8 (1976) , pages 97 to 100. Difluorocarbene is used in the production of insecticides, see U.S. Pat. No. 4,701,563. The preparation of difluorocarbene from PhHgCF.sub.3 and other compounds of this type is problematical from an environmental standpoint.
Trifluoroacetyl chloride is likewise an important intermediate in chemical synthesis. The reaction with trifluoroethanol leads to the corresponding ester which can be cleaved by hydrogenation into two molecules of trifluoroethanol. Trifluoroethanol is a solvent which can be used in drying and cleaning processes.
The preparation of difluorochtoroacetyl chloride from 1,1-difluoro-1,2,2-trichloroethane and oxygen under photochemical irradiation by quartz lamps is described in Examined German Patent Application No. DE 1,069,137; in which chlorine is used as additive, although this leads to the formation of undesired byproducts.